THROW vs. RAISERROR

According to the Differences Between RAISERROR and THROW in Sql Server:

Both RAISERROR and THROW statements are used to raise an error in Sql Server.

The journey of RAISERROR started from Sql Server 7.0; whereas the journey of the THROW statement has just begun with Sql Server 2012.

Microsoft is suggesting we start using the THROW statement instead of RAISERROR. The THROW statement seems to be simpler and easier to use than RAISERROR.

Yes, it is, but only since 2012. If you're using 2008R2, then it didn't exist.

The definitions of state and severity are clearly documented in the raiserror documentation